fix(audio): WAV dump drift improvements, acceptable state

WAV dump changes:
- Bypass ring buffer, render directly with synth_render()
- Frame accumulator eliminates truncation errors
- Skip pre-fill and fix seek for WAV dump mode
- Result: No glitches, -150ms drift at 64b (acceptable)

Timeline editor:
- Fix waveform tooltip position calculation
- Increase beat bar visibility (0.5 opacity)

Cleanup:
- Remove all drift debugging code from audio.cc and tracker.cc

Status: Acceptable for now, further investigation needed.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 14 insertions, 3 deletions

diff --git a/doc/AUDIO_WAV_DRIFT_BUG.md b/doc/AUDIO_WAV_DRIFT_BUG.md
index e22f4fa..050dd49 100644
--- a/doc/AUDIO_WAV_DRIFT_BUG.md
+++ b/doc/AUDIO_WAV_DRIFT_BUG.md
@@ -1,7 +1,8 @@
 # Audio WAV Drift Bug Investigation
 
 **Date:** 2026-02-15
-**Status:** ROOT CAUSE IDENTIFIED
+**Status:** ACCEPTABLE (to be continued)
+**Current State:** -150ms drift at beat 64b, no glitches
 
 ## Problem Statement
 
@@ -163,8 +164,18 @@ Eliminates cumulative truncation error.
 1. ✅ Measure WAV sample positions directly (Python script)
 2. ✅ Add render tracking debug output
 3. ✅ Confirm over-rendering (366ms per 10s)
-4. ⏳ Implement fix
-5. ⏳ Verify corrected WAV alignment in viewer
+4. ✅ Implement partial fix (bypass ring buffer, direct render)
+5. ⚠️ Current result: -150ms drift at beat 64b (acceptable, needs further work)
+
+## Current Implementation (main.cc:286-308)
+
+**WAV dump now bypasses ring buffer entirely:**
+1. **Frame accumulator**: Calculates exact frames per update (no truncation)
+2. **Direct render**: Calls `synth_render()` directly with exact frame count
+3. **No ring buffer**: Eliminates buffer management complexity
+4. **Result**: No glitches, but -150ms drift remains
+
+**Remaining issue:** Drift persists despite direct rendering. Likely related to tempo scaling or audio engine state management. Acceptable for now.
 
 ## Notes